The invention relates to a device for mounting two camshafts,in the cylinder head of a multi-cylinder in-line internal combustion engine of the type having four valves per cylinder.
On internal combustion engines with two overhead camshafts, there is generally a problem in arranging the cylinder-head screws in the cylinder-head housing in such a way that, whilst at the same time as symmetrical a hole pattern as possible is preserved, they are still accessible from the topside of the cylinder head.
To ensure this, it has already been proposed in German Patent Specification 2,324,530, for an internal combustion engine with a device of the relevant generic type, to arrange the bearing housings of the camshafts in respective transverse mid-planes of the cylinders and the cylinder-head screws laterally relative to these on the insides of the camshafts, in a housing plane extending between the cylinders. However, the accessibility achieved thereby presupposes further constructive measures to ensure that the camshafts are at a considerable distance from one another, this being equivalent to a large valve angle, and that no more than four cylinder-head screws are necessary to fasten the cylinder head. The known device is therefore unsuitable for use in cylinder heads of diesel engines, since because of the compact combustion space required these can be designed only with relatively small valve angles and high combustion-space pressures and ideally need six cylinder-head screws in order to fasten the cylinder head.
An object on which the invention is based is, therefore, to develop the known device or camshaft mounting, so that the valve position and consequently the shape of the combustion space and the number and position of the cylinder-head screws can be selected freely, largely independently of the camshaft mounting.
According to the invention, this object is achieved by providing that the bearing housings form, together with longitudinal webs and transverse webs, a camshaft bearing frame which is separate from the cylinder-head housing and which can be screwed to the cylinder-head housing.
As a result of the invention, a separation of the camshaft mounting and the cylinder head is obtained in an advantageous way, thus resulting in a simplification of the basic cylinder-head body, since there is no need for the hitherto cast-in camshaft mounting. Because the camshaft mounting and the cylinder head are separated, the camshaft bearing frame can be machined separately from the cylinder head, thus making production more efficient as a result of the use of machine tools specially adapted for separate production cycles.
Another advantage is that the positions of the valves and the number and position of the cylinder-head screws are independent of the camshaft mounting, so that it is possible directly to produce cylinder heads with four valves per cylinder and small valve angles and with more than four cylinder-head screws, which are particularly suitable for use in diesel engines.
Since there is no need for a camshaft mounting in the cylinder head, the height of the basic cylinder-head body can be reduced by an amount corresponding approximately to the assembly dimensions of the bearing housings. In a cylinder head with guide housings for the valve tappets, this means, for example, that the parting plane for resting the cylinder-head cover can be shifted approximately level with the top edges of the guide housings.
Moreover, a further advantage of the invention is that, for a repair, the complete "camshaft mounting" unit can be exchanged, so that, in order to carry out adjustment work, there is no longer any need to remove the cylinder head, as has been necessary hitherto for this purpose.
Insofar as the bearing frame is produced as a casting which rests by means of the two longitudinal webs on the lateral housing walls of the cylinder head, a further advantage is that the oil supply to the camshaft bearing points can be transferred to the bearing frame by means of a groove or bore cast in the longitudinal webs, thus making it possible to do away with the otherwise customary oblong-hole bore in the cylinder head housing.
It is also advantageous that the bearing frame makes it unnecessary to carry out the boring of the cylinder-head end walls which has hitherto been required for the machining of the bearing housings in the cylinder head, thus at the same time ensuring simpler sealing between the cylinder head and cylinder-head cover.
Finally, yet another advantage is that the camshaft mounting and cylinder head can be preassembled independently of one another, the preassembly of the camshaft mounting also including the connection of the spur wheels and the setting of the control times, so that during final engine assembly it is then merely necessary to insert the camshaft mounting as a single unit into the cylinder head, thus in particular also simplifying the setting of the control times in comparison with the conventional double camshaft mounting.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.